The uplink of a Long Term Evolution (LTE) system supports two modes of hybrid automatic repeat request (HARQ) operations: adaptive and non-adaptive HARQ. In the case of non-adaptive HARQ, the retransmission request is sent on a physical HARQ indicator channel (PHICH) through the transmission of a negative acknowledgment (NACK) signal. In the case of adaptive HARQ, which is activated by transmitting an acknowledgment (ACK) signal on the PHICH, according to the previous transmissions and depending on the resource scheduling of other users in the system, both the format and the frequency location of retransmissions are signaled by the physical downlink control channel (PDCCH) while overriding the PHICH.